1. Field of the Invention
The invention pertains generally to accessory sub-assemblies for electrical switching apparatus and, more particularly, to shunt trip or under voltage release accessory sub-assemblies for circuit breakers. The invention also pertains to electrical switching apparatus accessories. The invention further pertains to electrical switching apparatus, such as, for example, circuit breakers including an accessory.
2. Background Information
Electrical switching apparatus, such as circuit breakers, as well as transfer switches, network protectors and the like, are often equipped with accessories such as, for example and without limitation, shunt trip devices and under voltage release (UVR) devices. Such devices can be employed in a variety of ways to initiate a change in status of the apparatus such as, for example, to trip open the separable contacts of the apparatus in response to an electrical fault condition (e.g., without limitation, current overload; short circuit; abnormal voltage) or other external condition.
In view of the increasing market trend to reduce the overall size of the circuit breaker, the space which is available within the circuit breaker housing is limited.
Referring to FIG. 1, typically, a shunt trip device 2 (or UVR device (not shown)) includes a number of coils 4, a frame 6, a plunger 8 and a heel 10, which cooperate to form a substantially closed magnetic circuit. A plunger stem 9 is further extended (not shown) in response to movement of the plunger 8 to, for example, engage and pivot a trip bar (not shown) to cause a circuit breaker (not shown) to trip open separable contacts (not shown). When one of the two example coils 4 is energized with a sufficient voltage, magnetic flux 12 is transferred through the ferrous parts of the magnetic circuit. As shown in FIG. 1, a south (S) magnetic pole is generated at the heel 10 and a north (N) magnetic pole is generated at the plunger 8. This attracts the plunger 8 to the heel 10 and causes the plunger to move.
Typically, a shunt trip device contains an instantaneous coil, which can only be energized during a relatively short period of time. A typical UVR device contains a relatively larger coil, and can be energized for continuous duty. The shunt trip plunger is actuated when sufficient voltage is applied, and the UVR plunger is released when voltage is removed. Because of this opposite functionality and strategy, known shunt trip and UVR devices do not use the same coil frame and the same molded housing.
Accordingly, there is room for improvement in electrical switching apparatus accessories.
There is also room for improvement in electrical switching apparatus that employ one or more accessories.